1. Field of the Invention
The present invention relates to a method of production of a semiconductor module, more particularly relates to a method of production of a semiconductor module wherein external connection terminal pads for bonding with solder balls or other external connection terminals are electrically connected with the semiconductor chip by wires and wherein surfaces of the external connection terminal pads are exposed at the bottoms of recesses formed in a sealing resin layer sealing the semiconductor chip, external connection terminal pads, and wires.
2. Description of the Related Art
Known in the art is a plastic package type semiconductor module 100 shown in FIG. 8. This semiconductor module 100 has external connection terminal pads 106 for bonding with solder balls 104 serving as external connection terminals and electrically connected with a semiconductor chip 102 by wires 108. A sealing resin layer 110 is formed for sealing the external connection terminal pads 106, semiconductor chip 102, and wires 108.
In this conventional semiconductor module 100, there is the defect that the external connection terminal pads 106 are exposed flush with the surface of the sealing resin layer 110 and so the bond strength of the solder balls 104 bonded to the exposed surfaces is low. This is because the shear stress and other stress applied to the solder balls 104 concentrates at the bonded surfaces between the solder balls 104 and external connection terminal pads 106.
To eliminate this defect, for example, as proposed in Japanese Examined Patent Publication (Kokoku) No. 4-47977, there is known the method of exposing the external connection terminal pads 106 at the bottoms of recesses formed in the sealing resin layer 110 and bonding the solder balls 104 at those exposed surfaces. Due to this, the shear stress and other stress applied to the solder balls 104 is dispersed to the inside walls of the recesses in addition to the bonded surfaces between the solder balls 104 and external connection terminal pads 106.
The above proposed method will be explained further with reference to FIG. 9A to FIG. 9E.
First, as shown in FIG. 9A, external connection terminal pads 202 each comprised of an Ni layer sandwiched between one Au layer and another Au layer and a semiconductor chip mount 204 are formed on one surface of a metal substrate 200 by plating.
Next, as shown in FIG. 9B, one surface of the metal substrate 200 is subjected to a first etching. The external connection terminal pads 202 and the semiconductor chip mount 204 are covered by Au layers and therefore are not etched and function as etching masks, so the portions of the metal substrate 200 under the external connection terminal pads and the semiconductor chip mount 204 are left as projections 206.
Next, as shown in FIG. 9C, the semiconductor chip 208 is placed on the semiconductor chip mount 204 and is electrically connected with the external connection terminal pads 202 by wires 210.
Next, as shown in FIG. 9D, the semiconductor chip 208, external connection terminal pads 202, and wires 210 are sealed by a resin to form the sealing resin layer 212.
Next, as shown in FIG. 9E, second etching is performed to remove the metal substrate 200. Due to this, the surfaces of the external connection terminal pads 202 are exposed at the bottoms of recesses 214 formed in the sealing resin layer 212. The recesses 214 are formed by removing the projections 206 formed at the surface of the metal substrate 200 due to the first etching by the second etching.
By bonding solder balls as external connection terminals to the surfaces of the external connection terminal pads exposed at the bottoms of the exposed recesses 214, it is possible to improve the bond strength between the solder balls and the external connection terminal pads 202.
The above conventional method, however, requires that the etching be performed twice, so the production process of the semiconductor module becomes complicated.
Further, the heights of the projections 206 formed by the first etching directly determine the depths of the recesses 214 formed in the sealing resin layer 212 in the end, so it is necessary to strictly control the etching stop in the first etching so that the heights of the projections 206 reach predetermined values. Therefore, it is necessary to strictly control the first etching process.